The invention is directed to crystallized polyethylene terephthalate, PET, which contains silicon, and to a process for its preparation.
It is well known that some polymeric materials, for example PET, may only be used once in their original form.
There is not yet known an ecologically safe and economically effective process with which waste-PET, post consumer PET waste, may be regenerated and/or modified for a further use in the food industry (food contact substance).
All over the world a lot of waste-PET (post consumer PET waste) is collected and is just disposed. Therewith is created an environmental problem.
It is further known that waste-PET may not be burned in an environmentally friendly way, because among others carcinogenic benzopyrenes are formed.
It has been proposed to incorporate waste-PET into new, fresh PET, so-called “virgin”-PET. Thereby in maximum 5 parts by weight of waste-PET may be incorporated into 95 parts by weight of “virgin”-PET, to avoid adversely effecting the quality of the respective product.
In this technology a very high vacuum must be applied in order to remove the volatile, toxic contaminations; see the VACUREMA technology of the company Ere-ma in A-4052 Ansfelden/Linz in Austria.
It has also been proposed to cleave waste-PET into the components terephthalic acid and ethylene glycol. These components may be used again for the synthesis of PET. This process needs technically complicated devices and is correspondingly expensive.
In WO 03/104314 A1 there is described a process for processing polyester wastes, for example waste-PET. In this process neither a vacuum technology nor a cleavage into partial components is used.
In this process crushed, washed and dried waste-polyester flakes are heated to a temperature of 130° C.±5° C. At this temperature is added a defined modifying agent in an amount from 4% by weight to 6% by weight, referred to the total mass.
Then the obtained mixture is stirred for about 60 minutes at this temperature.
Then the mixture is introduced into an extruder, heated to a temperature from 240° C. to 250° C., and extruded. The extrudate is pelletized.
The obtained pellets are amorphous. These amorphous pellets may not be further processed by means of standard injection moulding technology, because they stick together during the preheating.
In WO 95/01471 there is described a process for producing soil-repellant and abrasion-resistant monofilaments for screen cloth having a diameter from 0.1 to 1.0 mm from a linear silicon modified polyethylene terephthalate. In this process there is incorporated from 0.15 to 5.0% by weight of polydialkylsiloxane by co-condensation into the chain of the polymer.
According to the example of WO 95/01471, the silicon containing polymer is prepared by polycondensation of the monomers dimethyl terephthalate and ethylene glycol with an addition of 3.9% by weight of polydimethyl siloxane and manganese acetate. An antimony catalyst is used as an essential component of said polycondensation process.
The process of co-condensation takes place in an autoclave at elevated temperatures and by using different pressures.
In U.S. Pat. No. 5,643,998 there is described a recyclable polymer which comprises a plurality of oligomer units. This polymer is obtained by a polymerization process.
It is an object of the invention to reduce the year-to-year increasing amount of waste-PET by transforming waste-PET into a convertible and demanded product.
It is a further object of the invention to provide a simple and cost advantageous process for the preparation of this new product.
This new product can be used as a substitution in industrial preparation processes where up to now “virgin”-PET is used.
With the present invention these objects can be met.